Liquid-cooled waveguide load



2 Sheets-Sheet 1 Filed Jan. 28, 1963 lnvem'or Kf/VIVET/r' A TREf/V 2Sheets-Sheet 2 Filed Jan. 28, 1963 Inventor KENNETH F. TREEN y ;7

Allorney United States Patent 3,241,089 LIQUID-COOLED WAVEGUIDE LOADKenneth Frederick Treen, London, England, assignor to InternationalStandard Electric Corporation, New York, N.Y., a corporation of DelawareFiled Jan. 28, 1963, Ser. No. 254,358 Claims priority, application GreatBritain, Feb. 16, 1962,

35/62 3 Claims. (Cl. 333-22) This invention relates to loads for thenon-reflective dissipation of radio frequency (RF) power in waveguides,and has particular, though not exclusive, application when the power tobe dissipated is of the order of kilowatts.

A load constructed according to the principles of the invention is oftapered form to give a good match to incident RF power over a broad bandin a waveguide, and is arranged to have liquid circulating through it asthe actual power absorber. The interior of the load is arranged tominimize in use the formation of pockets of stagnant liquid at thepower-source end of it, since such stagnant pockets might overheatenough to boil and rupture the walls. It is at the power source end ofthe load that such stagnancy might occur, as the liquid is introducedand exhausted at the other end.

According to the invention, therefore, there is provided a waveguideload including a vessel smoothly tapered from a large end to an apex andhaving inlet and outlet conduits near the large end for a continuousflow of liquid through the vessel, static means within the vessel todistribute the flow, and means in the said distributing means resistantto the liquid flow to cause turbulence in the liquid in the vicinity ofthe said small end.

Since overheating may also occur due to power absorption within thewalls of the load, they should be as thin as is consistent withstructural rigidity, and of a material which is transparent to RF power.

An embodiment of the invention will now be described with reference tothe accompanying drawings, in which:

FIG. 1 is a partially sectionalized plan view of a waveguide equippedwith an RF load;

FIG. 2 is a side view of part of the waveguide shown in FIG. 1; and

FIG. 3 shows an end view and a side view of a detail of the arrangementshown in FIG. 2.

Referring to FIG. 1, there is shown a tapered insulating vessel 1 whichconstitutes the outer jacket of a load located within, and bolted to awaveguide termination section 2. The vessel 1 is smoothly tapered downfrom a large end 3, where it has approximately the internal dimensionsof the waveguide, to an apex end 3a, where it has an indentation 4 forthe location and attachment by a suitable adhesive of a centrallydisposed tube 5. The tube 5 extends within the vessel 2 from adjacentthe large end 3, to the indented region of attachment 4 at the apex end3a. Adjacent the large end 3, the tube 5 is attached to an inlet waterconduit 6, and at the indentation 4, the tube is castellated at 7, (seealso FIG. 3). Exit conduits 8 provide an exit for water entering inletconduit 6. The end of the waveguide 1 is closed, to prevent RF leakage,by a copper gasket 9 clamped by a rigid plate 10, through which pass theconduits 6 and 8. An inductive iris 11 and adjustable capacitive screws12 at the other end of the waveguide 1 constitute matching for theslight geometrical discontinuity presented by the load to the powersource.

The vessel 1 and the tube 5 are made of fiber glass, which material hasa low coefiicient of absorption for power at frequencies of hundreds ofmegacycles.

In operation, water is fed to the inlet conduit 6, whence it flows downthe tube 5, through the apertures formed 3,241,089 Patented Mar. 15,1966 by the vessel 1 and the castellations 7, and thence via the outerjacket of the load to the exit conduits 8. A sufiicient head of water isfed to the load for the resistance of the apertures to cause, at leastlocally, a turbulent flow. This turbulence tends to prevent theformation of pockets of stagnant water at the apex end, and so should bepresent to ensure safe operation.

With reference to the load shown in FIG. 1 it is necessary to take intoaccount the total flow of water required to dissipate the maximumexpected RF power without overall overheating, the dimensions of theinner tube and its castellations needed to pass the said total flow withthe required degree of turbulence and the head of water available.

Referring to FIG. 2 which shows a side View of the waveguide equippedwith the load seen in FIG. 1, there are seen two inspection tubes 13,13. The presence of these tubes enables inspection of the apex end ofthe load during operation, reduces the electric field in the region ofthis end, and permits the insertion of probes to sample the RF field.Also the inspection tubes 13, 13 can serve as a safety release for waterin the event of the load rupturing or leaking. To cooperate in such arelease action, an RF window may be provided in the source end 14 of thewaveguide section 2. The diameters of the inspection tubes 13, 13 arechosen so that their cut-off frequency is above the operating frequencyof the waveguide 2, so that RF loss through them is negligible.

FIG. 3 shows an end view and a side view of the tube 5 before theattachment of its castellated end to the apex end of the vessel 1 and ofits other end to the inlet conduit 6 (FIG. 1).

Fiber glass is chosen as the material for the vessel 1 and the tube 5not only for its low RF absorption coefticient, but also because of itsrigidity, and facility of moulding. Of course other nonconductivematerials may be used, but it should be borne in mind that a high RFabsorption will tend to nullify the advantages given by the turbulentflow according to the invention in minimizing local overheating.

The provision of thermometers in inlet and exit conduits 6 and 8, and ofmeans for measuring the water flow will enable the measurement of RFpower dissipation in the water.

With tap-water circulating through the load, and copper foil screeningat the large end of it, RF power losses as low as 50 db below theincident power level have been measured at 2000 mc./s. This figure ShOWSthe efficacy of a load according to the invention in the almost completedissipation of the incident power.

Variations from the above-described embodiment without departure fromthe principles of the invention will readily occur to those skilled inthe art.

For instance, the tapering of the vessel 1 may be in one dimension only,the water may be circulated in the reverse direction through the load,liquids, or solutions instead of water may be used in the load, thevessel 1 may be conical for insertion in circular waveguide, or theremay be apertures near the end of the tube 4 instead of the castellations7.

While I have described the principles of my invention in connection withspecific apparatus, it is to be clearly understood that this descriptionis made only by way of example and not as a limitation to the scope ofmy invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. A waveguide load utilizing a flow of liquid coolant comprising:

a vessel smoothly tapered from a large end to a small end and having atleast one inlet conduit and at 3 4 leastone outlet conduit connected tosaid large end, normal to said waveguide adjacent to said small end ofwherebygacontinuous flowv of liquid may be forced said tube. t a rthrough said vessel along the axis thereof; means for mounting saidvessel in the waveguide; References Cited by the Examiner a tube,centrally disposed in said vessel, having one 5 end connected to saidinlet conduit and its other end UNITED STATES PATENTS connected to saidsmall end of said vessel, said other 3,040,252 6/1962 NOYak 33322 endhaving a serrated edge adjacent the inside sur- 3,044,027 6/1962 Chm eta1 333*22 face of said small end of said vessel; and said vessel havinga protuberance axially disposed at 10 FOREIGN PATENTS .said small end,which cooperates With said serrated l 576040 5/1959 Canada- :igie tocause turbulence of the liquid in said small OTHER REFERENCES I 2.AWaveguide load, according to claim 1, wherein: Freedman! Radio E icEngineering, May 1954, i i said serrated edge surrounds saidprotuberance. 15 Pages 35 rehcd upon} 3. A waveguide load according toclaim 1 further comprising other tubes attached to said waveguide, eachsaid ELI LIEBERMAN, Primary Examinerother tube having a cut-offfrequency exceeding the operating frequency of said waveguide, and beingdisposed HERMAN KARL SAALBACH Examiner

1. A WAVEGUIDE LOAD UTILIZING A FLOW OF LIQUID COOLANT COMPRISING: A VESSEL SMOOTHLY TAPERED FROM A LARGE END TO A SMALL END AND HAVING AT LEAST ONE INLET CONDUIT AND AT LEAST ONE OUTLET CONDUIT CONNECTED TO SAID LARGE END, WHEREBY A CONTINUOUS FLOW OF LIQUID MAY BE FORCED THROUGH SAID VESSEL ALONG THE AXIS THEREOF; MEANS FOR MOUNTING SAID VESSEL IN THE WAVEGUIDE; A TUBE, CENTRALLY DISPOSED IN SAID VESSEL, HAVING ONE END CONNECTED TO SAID INLET CONDUIT AND ITS OTHER END CONNECTED TO SAID SMALL END OF SAID VESSEL, SAID OTHER END HAVING A SERRATED EDGE ADJACENT THE INSIDE SURFACE OF SAID SMALL END OF SAID VESSEL; AND SAID VESSEL HAVING A PROTUBERANCE AXIALLY DISPOSED AT SAID SMALL END, WHICH COOPERATES WITH SAID SERRATED EDGE TO CAUSE TURBULENCE OF THE LIQUID IN SAID SMALL END. 